The flash memory medium is a memory IC (integrated circuit) that can store information semi-permanently after power supply is cut off. It is a nonvolatile memory, e.g. Nand Flash (Nand gate flash memory), etc.
A key encryption or decryption calculation method has a feature that a certain calculation on plaintext (or ciphertext) is carried out with a key to obtain ciphertext (or plaintext) which is different from the previous content.
A flash memory device based on existing technologies, including a nonvolatile memory, a flash controller, and an interface, transmits, reads, writes, and deletes information through a computer via this interface to the processor. The flash memory device includes a flash disk with a USB interface, a portable hard drive, a SD, a CF, and a Memory Stick. The key for information protection is usually a fixed value, and is stored in a nonvolatile memory. Because the nonvolatile memory itself can be read and written directly without authentication, there is a risk that the information stored in the flash memory may be decrypted.
As the rapid development of the information technology, mobile storage technologies and mobile storage products have also been improved greatly. Moreover, as the increasing popularization of Internet and e-commerce, people start to pay attention to the secure treatment of stored data and the restriction to user authentication. For example, the published Chinese Invention Patents ZL 01114762.8 entitled “A semiconductor memory device” and ZL 02151984.6 entitled “Method for realizing secure data storage and calculation storage using a mobile semiconductor memory device” provide a semiconductor portable memory device that has user authentication function and data encryption and decryption functions. It can carry out ID authentication to the user of this semiconductor memory device, and encryption protection to the information stored in this semiconductor memory device. The encrypted information will be decrypted when it is read out. However, this user authentication code or password is stored in the flash memory directly. As there is a direct electronic reading/writing method for the flash memory, the user authentication code can be read out directly and be decrypted easily. Therefore, in nowadays, this semiconductor memory device and data storage method cannot meet the need of secure data storage.